A recent study has given us interesting insights into how thyroid hormone test levels are affected by timing in a woman’s monthly cycle. 55 women were tested in a situation that mimicked estrogen levels during ovulation. As the study progressed, tests showed that when estrogen reached ovulatory levels, the thyroid-regulating hormone TSH levels rose as well.
At the beginning of these women’s cycles, their TSH levels averaged at 1.78 when tested. When the women’s estrogen levels peaked (similar to levels that would occur just before they ovulated), their TSH increased four-fold to 3.30. It’s interesting to note that 31 percent of women had a TSH above 4.0 during their peak estrogen timing.
Another aspect that should be noted is that these women also had an increase in free T3, which is the active thyroid hormone. What this increase tells us is that the TSH was also actively stimulating thyroid hormone production.
Why Did These Thyroid Hormone Levels Rise?
Generally, when TSH levels rise, it means the person is likely more hypothyroid. Basically, their brain is signalling their thyroid to make more of the hormone. Since active T3 hormone levels rose as well, it’s safe to assume that in this situation, this rise in TSH is unlikely to indicate hypothyroidism. Why is this? Generally, in cases of hypothyroidism, free thyroid hormones such as T3 and T4 end up decreasing, instead of rising.
This TSH change happens because their thytrophes (the pituitary cells that regulate the thyroid) contain estrogen receptors. When estrogen activates them, their response is to make more TSH. The TSH then causes the gland to up-regulate thyroid hormone production.
Since free T3 levels increase along with the TSH with this estrogen peak which would normally happen at midcycle, this suggests that the person’s TSH levels shouldn’t be looked at alone as a marker of thyroid function at that time.
To learn more about this study and when is the best time to have your thyroid levels checked, read the full post on drfionand.com here.